Ok, I got approached by my boss at work about the possibility of making a 36" mirror for observing from say several 8 inch mirrors (think an arrangement like James Webb). In thinking about this to me it seems that there are issues here about positioning the mirrors and ensuring that once ground, they form a parabola etc. So what are the thoughts on this? Can an amateur make a large mirror from smaller mirrors and what would it take? Just curious and I know what my reply was but I said I would inquire. -- Thanks! Jay
It was talked about in the early days of SPOC. IIRC it was going to be an assemblage of 5 or 6 smaller mirrors cemented to a base of some sort and ground and polished as a unit. But in the end we went with a single mirror. patrick On 26 Aug 2015, at 18:58, Jay inUT <jayleads@gmail.com> wrote:
Ok, I got approached by my boss at work about the possibility of making a 36" mirror for observing from say several 8 inch mirrors (think an arrangement like James Webb). In thinking about this to me it seems that there are issues here about positioning the mirrors and ensuring that once ground, they form a parabola etc. So what are the thoughts on this? Can an amateur make a large mirror from smaller mirrors and what would it take? Just curious and I know what my reply was but I said I would inquire.
-- Thanks!
Jay _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy
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That's the only way to do it, without active control. But it's essentially a single mirror that way, but missing much of it's surface and probably not any lighter than a monolithic mirror of the same equivalent aperture. On 8/26/15, Wiggins Patrick <paw@digis.net> wrote:
It was talked about in the early days of SPOC. IIRC it was going to be an assemblage of 5 or 6 smaller mirrors cemented to a base of some sort and ground and polished as a unit. But in the end we went with a single mirror.
Jay, it is possible but technicall difficult. All of the wavefronts from the constiuent mirrors must coincide to 1/4 wave, just like a monolithic mirror. The James Webb is an infrared telescope, meaning it operates at longer wavelengths than a visual telescope. The diffraction-limited tolerance is thus more lax for those mirrors, than for a visual telescope. Modern multi-mirror professional telescopes use active control of each individual segment to keep them all in-step. You'd need a similar arrangement for an amateur scope, just on a smaller scale. A multi-mirror telescope is essentially an interferometer. You end up with the resolution of the diameter of the array, with the light-gathering power of the sum of the individual elements. But keeping all of the individual surfaces in-place at a level of precision equal to a single surface is a daunting task. It would be easier, cheaper, and yield better results to just make a 36" telescope, in this instance. Good question, though! It's been one of the amateur's dreams for a century. On 8/26/15, Jay inUT <jayleads@gmail.com> wrote:
Ok, I got approached by my boss at work about the possibility of making a 36" mirror for observing from say several 8 inch mirrors (think an arrangement like James Webb). In thinking about this to me it seems that there are issues here about positioning the mirrors and ensuring that once ground, they form a parabola etc. So what are the thoughts on this? Can an amateur make a large mirror from smaller mirrors and what would it take? Just curious and I know what my reply was but I said I would inquire.
The figure of the mirror is held in place by the stiffness of the glass. With multiple mirrors you need a massive mirror cell or dynamic motors to constantly fight against the sag from gravity. In space it is easier because gravity is taken out of the equation. There was a professional telescope called the MMT which was arranged in a six gun fashion. But that was just to have something to do until the big onepiece of glass was ground, figured, and polished. So there is no real advantage in the long run. DT From: Jay inUT <jayleads@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Wednesday, August 26, 2015 6:58 PM Subject: [Utah-astronomy] Making a 36" from many smaller mirrors Ok, I got approached by my boss at work about the possibility of making a 36" mirror for observing from say several 8 inch mirrors (think an arrangement like James Webb). In thinking about this to me it seems that there are issues here about positioning the mirrors and ensuring that once ground, they form a parabola etc. So what are the thoughts on this? Can an amateur make a large mirror from smaller mirrors and what would it take? Just curious and I know what my reply was but I said I would inquire. -- Thanks! Jay _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. To unsubscribe go to: http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Then enter your email address in the space provided and click on "Unsubscribe or edit options".
Yes but, the Keck telescopes are multiple mirror telescopes. Multiple mirror telescopes do work. Future space telescopes, including the James Webb and the proposed 12 meter, are designed to multiple mirror telescopes. It's not just the weight and sagging. It's the accuracy with which they must be aligned. Typically mirrors must be no worse that 1/4 wave from ideal. That also applies to multiple mirror scopes. SJ On Thu, Aug 27, 2015 at 9:36 AM, daniel turner via Utah-Astronomy < utah-astronomy@mailman.xmission.com> wrote:
The figure of the mirror is held in place by the stiffness of the glass. With multiple mirrors you need a massive mirror cell or dynamic motors to constantly fight against the sag from gravity. In space it is easier because gravity is taken out of the equation. There was a professional telescope called the MMT which was arranged in a six gun fashion. But that was just to have something to do until the big onepiece of glass was ground, figured, and polished. So there is no real advantage in the long run. DT
From: Jay inUT <jayleads@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Wednesday, August 26, 2015 6:58 PM Subject: [Utah-astronomy] Making a 36" from many smaller mirrors
Ok, I got approached by my boss at work about the possibility of making a 36" mirror for observing from say several 8 inch mirrors (think an arrangement like James Webb). In thinking about this to me it seems that there are issues here about positioning the mirrors and ensuring that once ground, they form a parabola etc. So what are the thoughts on this? Can an amateur make a large mirror from smaller mirrors and what would it take? Just curious and I know what my reply was but I said I would inquire.
-- Thanks!
Jay _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy
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-- Siegfried
The U of A mirror lab has for the last 8 years been making the mirrors for the Giant Magellan Telescope which is comprised of seven 8.4 meter mirrors. The center mirror is a normal shaped mirror and the 6 outside mirrors are ground off center so when put together creates a mirror that is 25+ meters across. In 2009 when I spent time in Tucson I used to go to the mirror lab with Dean Ketelsen who was one of the lead opticians there. He retired a few years ago but as things are he still works there because there are very few in the world who can do what he does. When done the GMT will have adaptive optics and so the mirrors will be adjusted often depending on conditions of the sky.
-- Such a long long time to be gone, such a short time to be there.
Interesting coincidence, this week my daughter is visiting from the Bay area of California, where she works as a hair stylist. Just a few days before coming here, a walk-in client turned out to be the production manager of either the James Webb or Magellan scope at Lockheed (she wasn't sure), but was excited when he told her. "My dad would love to talk to you!". Haha. /R From: Robert Taylor <ratskradmt@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Thursday, August 27, 2015 11:00 AM Subject: Re: [Utah-astronomy] Making a 36" from many smaller mirrors
The U of A mirror lab has for the last 8 years been making the mirrors for the Giant Magellan Telescope which is comprised of seven 8.4 meter mirrors. The center mirror is a normal shaped mirror and the 6 outside mirrors are ground off center so when put together creates a mirror that is 25+ meters across. In 2009 when I spent time in Tucson I used to go to the mirror lab with Dean Ketelsen who was one of the lead opticians there. He retired a few years ago but as things are he still works there because there are very few in the world who can do what he does. When done the GMT will have adaptive optics and so the mirrors will be adjusted often depending on conditions of the sky.
-- Such a long long time to be gone, such a short time to be there. _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Send messages to the list to Utah-Astronomy@mailman.xmission.com The Utah-Astronomy mailing list is not affiliated with any astronomy club. To unsubscribe go to: http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Then enter your email address in the space provided and click on "Unsubscribe or edit options".
I was just reminded of the UofU Star Base project: http://www.physics.utah.edu/starbase Its just across the valley in Grantsville at the Sea Base. They use two 3 meter multiple mirror telescopes. They use an artificial star/laser to aim/calibrate the mirrors. Its not exactly a visual light telescope but you can see what goes into making a multiple mirror telescope, and the complexity of operation. I don't know if they give tours or not, but I hope this helps. Jamie B
Ok that will teach me to read fast, it is a visible light telescope and they use a spotlight 300 yards away as there artificial star. I sit or stand corrected. Jamie B
participants (8)
-
Chuck Hards -
daniel turner -
Jamie Bradley -
Jay inUT -
Richard Tenney -
Robert Taylor -
Siegfried Jachmann -
Wiggins Patrick